Gluten is a protein complex found in the triticeae tribe of grains, which includes wheat, barley and rye. The gluten content in wheat flour provides desirable organoleptic properties, such as texture and taste, to innumerable bakery and other food products. Gluten also provides the processing qualities familiar to both the home baker as well as the commercial food manufacturer. In short, gluten is considered by many to be the “heart and soul” of bakery and other food product.
However, gluten has its drawbacks. The gluten protein complex, upon entering the digestive tract, breaks down into peptide chains like other protein sources, but the resulting gluten-related peptide chain length is longer than for other proteins. For this and other reasons, in some people, these longer peptides trigger an immune response commonly referred to as celiac disease. Celiac disease is characterized by inflammation, villous atrophy and cryptic hyperplasia in the intestine. The mucosa of the proximal small intestine is damaged by an immune response to gluten peptides that are resistant to digestive enzymes. This damage interferes with the body's ability to absorb vital nutrients such as proteins, carbohydrates, fat, vitamins, minerals, and in some cases, even water and bile salts. If left untreated, celiac disease increases the risk of other disorders, such as anemia, osteoporosis, short stature, infertility and neurological problems, and has been associated with increased rates of cancer and other autoimmune disorders.
The early diagnosis of celiac disease, followed by treatment of celiac disease by eliminating gluten from the diet, leads to clinical and histologic improvement, thereby helping to reduce the probability that some of the associated, irreversible disorders will occur in a person diagnosed with celiac disease. A gluten-free diet is the mainstay of safe and effective treatment and management of celiac disease.
There are other medical reasons for following a gluten-free diet. People who are gluten-intolerant or gluten sensitive, which may include people diagnosed with Crohn's disease, ulcerative colitis, irritable bowel syndrome, dermatitis herpetiformis, or autism, are sometimes recommended or prescribed to follow a gluten-free diet. In addition, some people experience an IgE-mediated response or allergy to wheat protein. The prevalence of gluten as a potential allergen has resulted in the U.S. Food and Drug Administration being required to issue regulations regarding the definition and requirements in order for a product to be labeled “gluten-free” by 2008. Europe and Canada have regulations currently in effect which define “gluten-free” labeling for food products. Therefore, there is also a compelling need for a diet that would meet regulatory bodies' definitions of a “gluten-free” label.
Accordingly, there is an increasing need for gluten replacement systems in food products, which not only reduce or eliminate gluten in a product, but which also result in food products that are comparable to their gluten-containing counterparts. There are numerous gluten-free products on the market, but most of these products, such as gluten-free bakery products, have a poor taste and eating quality, provide poor nutrition, and are sold at a high price to the consumer.
Successful gluten replacement, therefore, provides a difficult challenge to the food manufacturer. This is due to the multi-faceted role that gluten plays as an ingredient in a vast array of food products.
One possible approach to making gluten-free food products is to remove the gluten from the gluten-containing ingredients. Examples of gluten-removing technologies are as follows:                Extraction using various solvents and solutions, such as ethanol, solutions of salts (including lithium chloride), and aqueous solutions of various pH;        Combined extraction/High Pressure Liquid Chromatography (HPLC) procedures;        Fractionation extraction;        Water washing (which is similar to extraction, and may be combined with precipitation);        Centrifugation and ultracentrifugation;        Enzyme treatments (such as enzyme-assisted hydrolysis);        Gluten recovery using sieves; and,        Emulsification/agglomeration.        
There are many potential problems associated with attempting to remove gluten from gluten-containing ingredients. First, gluten may not be completely removed from the ingredients, resulting in levels of gluten which may be unacceptably high for patients with celiac disease. Second, the removal of gluten from some ingredients may result in the removal of the functional polymers that these ingredients require in order to bring structure to food products. Third, the expense associated with removing gluten from gluten-containing ingredients on a commercial scale may result in food product prices that are unacceptably high for consumers.
Fourth, incomplete clean-up following extraction procedures may leave deleterious substances in the ingredients. Some extraction solvents and solutions are not safe for human consumption. Moreover, even extraction solvents and solutions that are safe for human consumption may leave unpleasant flavors or aromas in the food ingredients, or may lead to other unwanted results. For example, the incomplete removal of ethanol could depress yeast activity, and the changes in pH caused by certain extraction solvents or solutions could affect gelatinization temperatures.
A typical method for making gluten-free food products consists of using only ingredients derived from gluten-free starting materials. For instance, a bakery product may be made using a flour derived from a gluten-free food source, such as garbanzo beans, rather than a flour derived from a gluten-containing grain, such as wheat. Examples of gluten-free flours that may be used to make gluten-free bakery products are as follows: amaranth flour, arrowroot flour, brown rice flour, buckwheat flour, corn flour, cornmeal, garbanzo bean flour, garfava flour (a flour produced by Authentic Foods which is made from a combination of garbanzo beans and fava beans), millet flour, oat flour, potato flour, quinoa flour, Romano bean flour, sorghum flour, soy flour, sweet rice flour, tapioca flour, teff flour, and white rice flour. However, this is not a comprehensive list of all flours that may be used to make gluten-free bakery products. Frequently, different gluten-free flours are combined to make a bakery product.
Examples of other possible ingredients in gluten-free bakery products, besides gluten-free flours, are as follows: starches, including potato starch and cornstarch; gums, including xanthan gum and guar gum; gelatin; eggs; egg replacers; sweeteners, including sugars, molasses, and honey; salt; yeast; chemical leavening agents, including baking powder and baking soda; fats, including margarine and butter; oils, including vegetable oil; vinegar; dough enhancer; dairy products, including milk, powdered milk, and yogurt; soy milk; nut ingredients, including almond meal, nut milk, and nut meats; seeds, including flaxseed, poppy seeds, and sesame seeds; fruit and vegetable ingredients, including fruit puree and fruit juice; and flavorings, including rye flavor powder, vanilla, cocoa powder, and cinnamon. However, this is not a comprehensive list of all ingredients that can be used to make gluten-free bakery products.
Most approaches to formulating gluten-free products involve the use of starches, dairy products, gums and hydrocolloids, and other non-gluten proteins. These materials tend to be hydrophilic and thus may require excessive amounts of water; in fact, the unbaked material is often a batter that is poured into the pan. During baking, the high water content leads to more fully pasted starch and in turn a more brittle, crumbly final texture and a shorter, less chewy bite. In some cases the final product is even starch continuous, which is the opposite of gluten-containing bread.
Gluten is a cohesive protein mass containing primarily two groups of protein subunits—the lower molecular weight monomeric gliadins, having a molecular weight of between about 30,000 to about 125,000, and the higher molecular weight polymeric glutenins, having a molecular weight of between about 100,000 to 3,000,000 or higher.
Gluten contains both hydrophilic and hydrophobic amino acids, giving the protein mass both properties. Upon hydration, gliadins are viscous and extensible—they flow with gravity. As a result, gliadins are often considered plasticizers. Glutenins, on the other hand, upon hydration become very elastic, that is, they have a memory and are capable of returning to the original shape or approximately the original shape following deformation. This combination of properties of gluten imparts the cohesive and viscoelastic properties of a dough containing gluten, and provides the dough with gas-holding properties beneficial for successfully making bakery products.
The protein composition of gluten also includes both ordered and random regions, short and long chain proteins, and linear and branched chains. This combination of opposing properties makes gluten an important component of the manufacturing and final qualities of bakery products, and is why it has been so difficult to replace gluten with other ingredients and still produce a suitable final bakery product.
Gluten-containing bakery products begin with a gluten-containing dough. To make the dough, the ingredients are mixed with a liquid, such as water, and the continued mixing of the dough creates gas cells in the dough. As a result of mixing, the hydrated gluten forms a continuous phase in the dough, which encapsulates and stabilizes the gas cells created in the dough. When the leavening agent in the bakery product begins to generate carbon dioxide, the carbon dioxide first dissolves into the liquid phase of the dough, but upon saturation of the liquid phase, enters into the gas cells, causing the cells to expand. Gluten provides the necessary strength and flexibility to stabilize the gas cells as they expand.
When a dough containing gluten is baked, the temperature and volume of the dough begin to increase with time, until the volume reaches a plateau. As baking progresses, there is a major change in the water balance of the bread system. The starch gelatinizes and becomes hygroscopic. Amylose exudes from the starch granules; however, the granules remain largely intact because water is limited and unable to fully paste the starch. Gas cells become larger because the volume that a gas occupies is related to its temperature. This stretches the gluten, which enables the gluten polymers to align, and in turn, strain harden. Eventually the system fails and the cells break, resulting in a bicontinuous bread system; the air and gluten are continuous and the starch is discontinuous. With zero pressure gradient, the bread does not collapse. Upon cooling, the viscosity of the starch gel in the crumb increases and the structure sets. The continuous, polymerized and strain-hardened nature of the gluten and the discontinuous nature of the starch provide the final bread structure having a desirable specific volume and chewy texture.
Gluten, therefore, is a very dynamic component of a bakery product system. In its hydrated form in a dough, gluten forms the viscoelastic gas-retaining matrix that is needed in order for the dough to attain the characteristics that will result in a successful bakery product. To achieve the final bread structure, a physical strain hardening and a chemical cross-linking or polymerization occurs. Upon baking or other types of heating, gluten loses moisture, becomes polymerized, and strain hardens, thereby setting the texture and volume of the bakery product.